Lithium-ion batteries (LIBs) have attracted extensive attention in the past two decades for a wide range of applications in portable electronic devices such as cellular phones and laptop computers. Due to rapid market development of electric vehicles (EV) and grid energy storage, high-performance, low-cost LIBs are currently offering one of the most promising options for large-scale energy storage devices.
In general, a lithium ion battery includes a separator, a cathode and an anode. Currently, electrodes are prepared by dispersing fine powders of an active battery electrode material, a conductive agent, and a binder material in an appropriate solvent. The dispersion can be coated onto a current collector such as a copper or aluminum metal foil, and then dried at elevated temperature to remove the solvent. Sheets of the cathode and anode are subsequently stacked or rolled with the separator separating the cathode and anode to form a battery.
Characteristics of electrodes can dramatically affect performance and safety characteristics of battery. Over the last decades, cathode materials have attracted a lot of attention since they affect capacity and energy density of a battery. Anode material is also critical for charging, low temperature and safety performance of batteries. A smooth and uniform coating layer on anodic current collector is less susceptible to dendrite formation, which can extend the cycle life of the cell and enhance the safety of the cell. Therefore, preparation of the anode slurries is an essential first step towards the production of good quality batteries.
Residual solvent in the coating layer due to incomplete drying can contribute to adherence problems which will eventually affect the performance and quality of the batteries. One way to remove residual solvent from an electrode is to dry the electrode for a long period of time under high temperature. However, prolonged heating at high temperature may cause the coating to disintegrate due to aging of polymeric binder. The change of electrode characteristics is detrimental to the proper functioning of the completed battery.
Currently, much research and development is being performed related to electrode slurries. CN Patent Application No. 105149186 A describes a method for drying the electrode coating. The coated electrode is inductively heated by an induction heating coil to heat the metallic current collector to a desired temperature. However, the coated electrode may be non-uniformly heated due to nonuniform distribution of induced current density in the coil. This can create a problem with respect to obtaining rapid heating to a uniform temperature, affecting the quality of the coating.
CN Patent Application No. 102544461 A describes an anode material of a lithium-ion battery. The anode material comprises a crystalline silicon powder, carbon black and binding material. The particle size of the silicon powder is between 2.0 μm and 5.0 μm. However, 15-20 wt. % of binding agent is needed for binding the anode active material and conductive material to the anode current collector because of high specific surface area of the anode active material. A large amount of binding agent in the electrode coating will reduce the energy density of a lithium-ion battery. Furthermore, the resulting anode is required to be dried in a vacuum dryer at high temperature for 12-24 hours. The long time required for drying is considered to be not suitable for large scale production.
CN Patent Application No. 101154720 A describes an anode slurry for lithium-ion battery. The anode slurry is made of a nano-carbon material, a weak acid, a binder and a solvent. The average particle size of the nano-carbon material ranges from 20 nm to 70 nm. However, there is no mention of conditions for drying the coated anode slurry. Furthermore, capacity loss of the battery comprising the anode coated with this anode slurry is 7-15% of its initial capacity after 300 cycles at 1 C/1 C.
In view of the above, there is a need for a continuous improvement of the anode slurries with homogeneous ingredient dispersion and quick drying capability for battery performance and manufacturing efficiency reasons.